1. Field of the Invention
This invention relates generally to a method and apparatus for monitoring etching, and more particularly to a method and apparatus for monitoring etching which is suitable for monitoring the state of progress of etching of a sample to be etched by a dry etching process.
2. Description of the Prior Art
An etching apparatus for treating a sample by a dry etching process such as a plasma etching process is disclosed, for example, in Japanese Patent Laid-Open No. 84431/1983. In this apparatus, a discharge portion for detecting the intensity of an emission spectrum is disposed afresh on the downstream side of the flow of a reactive gas with respect to an etching portion where the sample is to be etched by plasma.
The apparatus described above controls the discharge of the discharge portion independently of the etching portion, and introduces the gas generated by etching in the etching portion into the discharge portion and discharges the gas so that an inherent emission is generated efficiently and the decrease of the concentration of an active group due to etching is susceptibly responsive to the change of intensity of the emission spectrum.
However, this apparatus does not particularly consider how to control the gas pressure of the discharge portion. In other words, since the discharge portion is disposed at an exhaust pipe portion where the gas pressure is not at all controlled, the bright line spectrum at the discharge portion will become ambiguous if the emission line spectrum occurring at the etching portion is ambiguous, particularly when the same method of applying an electromagnetic field is employed for both the etching portion and the discharge portion. Therefore, the state of etching of the sample at the etching portion can not be monitored with a high level of accuracy.